The present invention relates to a video tape recorder and, more particularly, to a still vision recording and reproducing system for use in video tape recorder.
The still vision recording and reproducing system generally includes a field memory and a recording device. The input of the field memory is selectively connectable to either one of a source of video, or television, signal and the output of the recording device, and the output of the field memory is selectively connectable to either one of a television signal processing stage or the input of the recording device. When the system is in the recording mode, the input and output of the field memory are connected to the television signal source and the input of the recording device, respectively, for temporarily memorizing the television signal of one field in the field memory, and sequentially reading out and recording the temporarily memorized television signal in the recording device. Since the recording device has a certain capacity, it may record a plurality of fields of television signal by carrying out the memorizing operation repeatedly. Then, when the system is in the reproducing mode, the input and output of the field memory are connected to the output of the recording device and the television signal processing stage, respectively, for reading out the recorded television signal in the designated section in the recording device, and temporarily memorizing the read out television signal in the field memory. The television signal thus memorized in the field memory is sequentially taken out repeatedly and applied to the television signal processing stage to produce a still picture on a cathode ray tube.
In the above arrangement, since the field memory generally includes shift register and memory unit, such as RAM, the television signal is converted into digital form before it is applied to the field memory. For example, the television signal is converted into digital form with sampling rate at frequency of 10 MHz and quantization level of 6 bits per each sampling. Therefore, it is understood that the digital television signal is sent to the field memory at the rate of 60 megabits per second. Since it takes 1/60 second to send one field, the field memory is arranged to memorize 1 megabit. Thereafter, the memorized digital television signal is sequentially sent to the recording device at a rate much slower than the original rate.
Furthermore, for the recording device, it has been a common practice to employ a so-called foil-, or floppy-, disc recorder. The floppy-disc recorder includes a thin film disc that rotates at a high speed, e.g., 360 rpm. The thin film disc has a plurality of tracks, such as 77 tracks, on each of the opposite faces, and is capable of recording 250 to 500 kilobits per second. When the employed floppy-disc recorder is a type that records 500 kilobits per second and rotates the film disc at 360 rpm, it can record 500.times.10.sup.3 .times.1/6.times.0.9=75.times.10.sup.3 (bits) in each track, provided that 0.9 is an effective utilizing rate of each track. Therefore, in order to memorize television signal of one field, it is necessary to use (10.sup.6 .div.75.times.10.sup.3 =13.3) 14 tracks.